Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X35: Free-Surface Flows: Water-Entry |
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Chair: Christine Gilbert, Virginia Tech Room: 355 A |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X35.00001: Making a Splash: Experimentally Modeling a Single Slamming Event of Planing Craft Ben Darden, Christine Gilbert Slamming into waves can cause structural damage to high-speed planing craft, as well as hinder or injure onboard personnel. As such, it is one of the main limiting constraints of high-speed surface vessels' operating envelopes. The controlled motion experiments presented in this talk allow for the capture of a single slam event, allowing for a deeper study of the effects of hydrodynamic loads occurring in a slam. A planing hull model, attached to a moving carriage, was subjected to controlled vertical motions using two linear actuators to resemble real-life slamming motions but in a rotated frame of reference. The system allows for the trim angle of the model to be adjusted. Hydrodynamic forces are measured globally and pressures were measured at locations near the bow. With this configuration, the maximum forces and peak pressures experienced by the model increased when slammed at higher total velocities relative to the free surface. However, slams into the water at steeper impact angles resulted in a decrease in forces and pressures. Experiments fixed the body orientation during the slam event. The results from this study can aid in new tools that can be used to evaluate slamming for the design of small craft. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X35.00002: Entry and exit dynamics of symmetrical projectiles David Charland, Abraham Thayer, Megan C. Leftwich Amphibious drones are a type of unmanned vehicle that can both fly and swim. Typically, these drones will hover above the water then gently land on the surface. We are investigating the possibility of amphibious drones that can dive straight into and out of the water without slowing down. In this study we investigate symmetrical projectiles in canonical shapes—a sphere and a cone—that are driven into and out of a tank of water at a high Reynolds Number, roughly matching that of common military and commercial drones. There is an extensive body of research on entry body dynamics, however this study adds the exit dynamics as well. A closed motor-pulley system with the projectiles attached to a ⅛ in wire drives them out of the water at about 55 m/s. Images of the projectile, air cavite and splash are captured by a high speed camera at 6000 frames per second. We measure the forces on the object as it crosses the surface of water into air and observe the post-exit flight. The high speed images determine how changing the aspect ratio of the projectile affects the splash as the object exits the water. This shows that there is less water entrainment into the air, making it easier for the object to exit the water and maintain its speed. The amount of water entrained from the exit is examined in the same manner as air for entry body dynamics in cavity formation. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X35.00003: Impact forces of projectiles with varied cone-angles into non-Newtonian fluids Charbel El Khoury, ABHIJIT KUMAR KUSHWAHA, Tadd T Truscott Several researchers set out nearly 100 years ago to understand the impact of projectiles into water with varied cone angles and cusps. Recently researchers have found the cone angles that maximize and minimize impact forces and have even suggested several other methods of reducing impact forces. However, when the fluid is changed to non-Newtonian we find that the forces are different as expected. By methodically varying the cone angle of the projectile tip, imbedding accelerometers, and tracking high-speed camera images; we are able to study the various effects on the cavity formation, depth, and drag forces. Together, the data provides a clearer understanding of the underlying physics and changes that a non-Newtonian fluid causes. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X35.00004: Real-Time Prediction of Slamming Loads on High-Speed Planning Craft Using Extended LSTM Networks John Gilbert, Christine Gilbert, Ahmed Ibrahim, PhD, Carolyn Judge, PhD Slamming loads, characterized by severe impacts during vessel interactions with the water surface, pose significant challenges to the structural integrity and safety of high-speed marine vessels. This study leverages extended Long Short-Term Memory (xLSTM) networks, which incorporate enhanced memory capabilities and attention mechanisms, to develop real-time predictive models for slamming loads. These models consider critical factors such as hull shape, vessel state, and incoming wave field dynamics. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X35.00005: CyberDiver: an untethered robotic platform for water-entry experiments John Thomas Antolik, JESSE L BELDEN, Eli Silver, Tristan Keyser-Parker, Daniel M Harris High-speed water entry of solid bodies has been a subject of intense investigation for over a century, featuring rich multi-scale physics and high relevance to engineering applications. Several recent works have extended the classical understanding of water entry dynamics – in which impactor speed and geometry are the primary independent variables – to the case of a flexible impactor with one or more elastic degrees of freedom, showing that flexibility can significantly influence the impact force. The CyberDiver enables the further possibility of not just passive, but active motion during water entry experiments, inspired by examples in the biological world such as sea birds that tuck their wings at impact or Olympic divers performing a "rip" entry. The CyberDiver is simplified to a single axial degree of motion that is driven by a linear motor and dropped into a quiescent water bath with normal incidence. The relative position and coupling force between an axisymmetric nose piece and cylindrical trailing body can be prescribed in relation to the moment of impact, and the resulting impact force, splash and cavity dynamics analyzed. Furthermore, high-bandwidth onboard sensing of the nose displacement and coupling force enables the CyberDiver to operate as an untethered cyber-physical system, permitting an arbitrary structural coupling that is designed in software to be experimentally tested and exposed to the complete set of impact physics. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X35.00006: Computational study of asymmetric water entry of cylindrical solid objects: Effects of tilt angle and nose curvature Kartik Gupta, Mehdi Raessi, Jesse L Belden Water entry of solid objects occurs asymmetrically in many applications, where the leading edge of the object may be tilted relative to the free surface. Under this asymmetric condition and depending on the tilt angle, the dynamics of water entry can be significantly different from those of perfectly symmetric water entry, i.e., a tilt angle of zero. Furthermore, in such asymmetric water entry, there is an interplay between nose curvature effects and tilt angle. Using an in-house multiphase flow solver, we performed simulations of water entry of cylindrical solids with various nose curvatures and at small tilt angles. Although the solid is initially tilted, it has the freedom to rotate and orient itself vertically. We present the effects of tilt angle and nose curvature on splash formation, cavity formation, and cavity closure. Air and water velocity fields near the solid nose are profiled. In addition, the results include quantification of solid deceleration and air entrapment as a function of tilt angle and nose curvature. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X35.00007: The role of nose geometry on the slamming forces during the water entry of a simple harmonic oscillator Tristan Keyser-Parker, John Thomas Antolik, Ela Lucas, Ashley Kraekel, JESSE L BELDEN, Daniel M Harris When a solid body impacts an air-water interface, substantial fluid-induced forces may arise that can potentially be detrimental to the impactor. In recent prior work, we demonstrated that introducing an elastic coupling between an impacting hemispherical nose and trailing body can consequently decrease or increase the peak force experienced by the body as compared to the fully rigid case, with the outcome depending sensitively on the parameters. Here, we extend the investigation to axisymmetric impactors with various conical noses, documenting how the threshold between force decrease and increase depends on the cone's opening angle. The acceleration of both the nose and the body during the impact event are directly measured using custom onboard inertial measurement units. Our experimental measurements are compared to predictions from a reduced-order model that considers the excitation of the impactor's elastic mode in response to the hydrodynamic slamming forces arising from the added mass effect. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X35.00008: The Impact of a Flexible Plate on a Wavy Surface Samuel E Lee, James H Duncan, Kenneth Thomas Kiger, Miao Yu, Ezekiel Salvo The oblique impact of rectangular aluminum plates (length 108 cm and width 41 cm) on a wavy water surface are studied experimentally as a prototypical geometry for better understanding the strong nonlinear coupling of elastic objects as they impact a fluid domain. The plates are mounted at an angle inclined 10 degrees above the still water surface (leading edge up) via a 6-component dynamometer frame to a translational carriage capable of both horizontal and vertical motion. Previous experiments were performed with plates impacting a quiescent water surface while varying the impact kinematics, effective plate stiffness, and impact time scales. It was found that the loading and deformation was controlled by the plate's local inclination angle at the instantaneous position of the spray root where the plate intersects the water surface. In the present experiments, oblique impacts on a wavy surface are explored during which a large portion of the plate surface is nearly parallel to a section of the dynamically moving water surface. The wavy surface consists of a single frequency sinusoidal wave train with wavelengths on the order of the plate length. The direction of wave travel is opposite to the direction of the plate's horizontal motion. The plate kinematics, wave height, and impact location along the wavelength are varied. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X35.00009: Vertical water entry of a long cylindrical rod with zero inclined angle: crater dynamics and droplet generation Chang Liu, Erik Kiger, James H Duncan The vertical impact of a long cylindrical rod with zero inclined angle (parallel to the water surface) on a quiescent water surface is studied experimentally. We focus on examining the crater dynamics and the droplets produced only as a direct result of pinching off as the crater collapses. Three solid steel cylindrical rods are used in the current study, with the same length of 91.4 cm and different diameters of 0.635, 1.270 and 1.905 cm, respectively. Electromagnets are used to attach and release each rod from a fixed height of 15 cm above the water surface, corresponding to a free-fall entry speed of 1.72 m/s. A hydrophobic coating is applied on the surface of each rod to guarantee the formation of a relatively smooth 2D crater. The evolution of the crater profiles is measured by laser induced fluorescence (LIF) imaging technique and the retraction speed of the crater tip formed right after pinch-off occurs is measured using back-lit diffuse light movies. The droplets produced are measured with an in-line cinematic holographic system. The positions, diameters (d ≥ 100 μm), times and velocities of droplets are measured as they move up across a prescribed horizontal measurement plane. Preliminary results show that as the rod diameter increases, the depth and width of the crater profile at pinch-off moment and the retraction speed of the pinch-off tip increase, which seem to be responsible for the observed increased number of produced droplets. The distributions of droplet size and velocity components are also presented. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X35.00010: Fluid dynamics of Manu jumping Kai Yung, Pankaj Rohilla, Daehyun Choi, Halley Wallace, Juhi Deora, Saad Bhamla New Zealand has popularized a technique for creating the biggest splash: Manu Jumping. Divers fold their body in a "V formation" and snap open to a "flat formation" upon water entry to generate a large air cavity. We investigate the multiple factors that determine the characteristics of cavity formation and resultant Worthington jet, which is crucial to splash generation. Our experiments vary size, shape, and impact speed of solid bodies and their effects on the Worthington jet dynamics. We analyze Manu Jumping in humans and physical models. To study the Manu Jumping technique underwater, we created a diving robot which mimics the human technique of opening underwater to maximize cavity size. We uncover the water entry parameters and scaling laws that Manu Jumpers dive into when they create the biggest splash. |
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